1. Technical Field
This invention relates generally to insulators for vehicle exhaust systems and more specifically to an insulator for a vehicle exhaust system that includes a shield that snaps onto the insulator to protect it from excessive heat build-up and consequent possible failure due to heat damage.
2. Background Information
As motorists drive their vehicles over roads, they encounter potholes, bumps and other uneven surfaces that shake and jolt the vehicle body. These vibrations and jarring shocks to the vehicle body may cause damage to various components and connections. One of the systems of the vehicle that may be damaged by such vibrations is the exhaust system. The vibrations may cause cracks in the welds between components of the system.
In order to dampen these vibrations and to reduce the potential side effects, manufacturers have customarily used rubber vibration insulators or dampers in the connections between the exhaust system and the vehicle chassis. These vibration dampers have worked fairly well until recently.
In the past, exhaust systems on automobiles included fairly long, straight sections of pipe that allowed air to flow freely and rapidly from the engine to the exterior. Hangers connected the exhaust pipes to the vehicle bodies and dampers were located periodically along the length of these pipes to support the system and insulate occupants from vibration in the pipes. The exhaust system allowed exhaust gases to escape from the vehicle and also allowed heat from the engine to be rapidly dissipated.
Specifically, elastomeric hangers provided a number of benefits, including retention of the exhaust system to the car, as well as providing a flexible attachment that could accommodate expansion and contraction of the exhaust system as a result of heating and cooling during vehicle operation. Still further, these elastomeric bushings would isolate vibrations in the system and system noise from reaching the vehicle occupants.
Problems with this system began to appear with the introduction of catalytic converters. Catalytic converters are used to reduce the release of noxious gases into the atmosphere. They tend to work best if they are heated and consequently they are located as near to the engine block as possible, but sufficiently far away to prevent the device from overheating and being damaged. Exhaust gases are hottest when they exit the engine and manufacturers have utilized this heat to heat up the catalytic converters to improve their performance. Sometimes manufacturers preheat the catalytic converter using a small electric resistance heater. Catalytic converters restrict the free airflow through the exhaust system. The noxious gases are filtered out, but the converters drastically reduce the rate of heat loss through the exhaust system. Heat tends to build up in the area surrounding the catalytic converter and through the rest of the exhaust system. As the catalytic converter slows the air flow through the exhaust system, the rate of heat loss from the system decreases and consequently there is a greater increase in the temperature of the exhaust pipes. This heat build-up in the rest of the system may result in the vibration insulators becoming overheated and damaged. The insulator may fail, resulting in an increase in disturbances from the exhaust system and ultimately in damage to or loss of the exhaust system itself.
Manufacturers have attempted to shield components from the heat build up caused by the reduction in the exhaust gas flow rate. Their attempts have included the use of metallic heat shields positioned above the catalytic convertor and along the exhaust system in order to prevent heat from entering the cab of the vehicle and to prevent fires and the like when heat is positioned adjacent to wire harnesses or other flammable material. Metallic shields are expensive to manufacture and fairly difficult to install if a problem is diagnosed. As such, these shields have not been utilized to protect exhaust insulators or vibration dampeners. As the exhaust system is relatively cheap to replace, this type of shield has not traditionally been used to protect the exhaust system. Other possible solutions to this problem have been the use of air spaces or gaps to separate components from each other, as well as the use of double layer exhaust pipes which include an air space between the two layers. However, these solutions have been fairly costly and it has been difficult to retrofit cars with these systems. The industry desires a device that addresses these problems.